This project has identified a wide range of alterations in plasma membrane lipids and proteins which are associated with differentiation of lens epithelial cells to form lens fibers. Results have shown that phosphatidylinositol degradation ceases when lens epithelial calls differentiate to form lens fiber cells, while synthesis of phosphatidylinositol and other phospholipids increases. Since phosphatidylinositol is rich in arachidonic acid, a precursor of prostaglandins and leukotrienes, the metabolites of arachidonic acid produced by lens cells have been characterized. Loss of a lipoxygenase pathway metabolite has been correlated with the initiation of differentiation in vitro. Plasma membrane proteins which have been investigated include the insulin and IGF receptors and the membrane associated protein, calpactin I. Equilibrium binding studies have shown chat embryonic chick lens epithelial cells possess both insulin and IGF I receptors, and that expression of both is regulated during differentiation and development. Analysis of membrane associated proteins has demonstrated that calpactin I is a major component of the EDTA extractable protein of lens membranes. mRNA for this protein accumulates during in vitro differentiation, in parallel with an increase in immunofluorescence staining intensity. These studies have shown that embryonic chicken lens epithelial membranes are dynamic entities which undergo structural and functional changes as part of the differentiation process.